I looked at your video a half dozen times. I think you are doing the scalp exercise the right way. There is plenty of scalp movement when you contract the scalp muscles. There is also good ear movement which indicates you are getting a contraction out of both the frontalis and occipitalis muscles. I may be wrong about this but I think I notice a little contraction of the frowning muscle when you contract the frontalis muscle at the front of your head. In other words, there might be a small contraction of the procerus that makes your eyebrows come together. But that is a trivial criticism. In general, the way you do the scalp exercise looks perfect to me.